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Why Japan's Coordinate System Is Uniquely Complex
Japan has three active datum layers: the legacy Tokyo Datum (EPSG:4301), the 2000-era JGD2000 (EPSG:4612), and the current JGD2011 (EPSG:6668). The Tokyo Datum's shift from modern geocentric systems is massive, typically 450 to 700 metres depending on region. Even using JGD2000 data in Tohoku after 2011 without applying the coseismic correction can introduce errors of 0.5 to 1 metre.
GSI mandates use of the official grid files tky2jgd.gsb and touhokutaiheiyouoki2011.gsb via EPSG operation 6714 for professional surveying work. Any simplified Helmert approximation introduces residuals of 10, 0m, unacceptable for cadastral or infrastructure applications.
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地殻変動と再施工リスク：NAD83 vs WGS84の累積誤差
北米プレートは年間約2cm移動するため、NAD83(2011)とWGS84(G1762)は現在2.2メートル以上乖離しています。 高精度なNAD83地籍杭打ちに「標準的な」GPS WGS84座標を使用したことで、基礎のやり直しやインフラの配置ミスによる5万ドルの専門家責任賠償請求が発生しています。